ENVIRONMENTAL IMPACTS

OF GEOTHERMAL ENERGY

1

OF GEOTHERMAL ENERGY

Based on A Guide to Geothermal Energy and the Environment GEA

and The Environmental Impact of the Geothermal Industry CRES

Contents

Introduction

Geothermal Energy and the Environment Air Emissions

Solid and Liquid Waste

Noise Pollution

2

Solid and Liquid Waste

Noise Pollution

Water Quality and Use

Land Use

Geysers, Fumaroles and Geothermal Resources

Impact on Wild life and Vegetation

Summary

Conclusion

Introduction3

Geothermal energy is renewable resource. Unlike wind and solar resources,

which are more dependent upon weather fluctuations and climate changes,

geothermal resources are available 24 hours a day, 7 days a week.

Geothermal energy is the heat of the earth. Medium and/or high Geothermal energy is the heat of the earth. Medium and/or high

temperature geothermal systems are classified either as hydrothermal

systems (low or high enthalpy), which are encountered in specific locations

associated with the presence of fluids and permeability within the earth, or

as enhanced geothermal systems, which can be engineered everywhere.

IntroductionGeothermal Heat Pumps

4

Geothermal heat pumps utilize the heat content of the upper part of the earth,

and do not have any adverse environmental impact related to the geothermal

energy itself. However, as heat pumps, they need considerable quantities of

electricity for their operation and they contain refrigerants of very high electricity for their operation and they contain refrigerants of very high

greenhouse potential, in case they leak to the environment. Therefore, their

environmental impact is limited to contribution to the greenhouse effect due to

electricity consumption and due to possible refrigerant leakages. Due to the

higher efficiency of the geothermal heat pumps (COP = 4 to 6) compared with air

source heat pumps (COP = 2,5 to 3,5) and fossil fuels (efficiency = 80-90%),

overall impact to the greenhouse effect is significantly less than burning fossil

fuels or using air source heat pumps.

IntroductionEnhanced Geothermal Systems (EGS)

5

In the case of EGS, where water is initially injected and then circulates through the system,

not only zero CO2 emissions are foreseen, but also none of the other problems are

anticipated. However, it pays to engineer EGS within or just outside the boundaries of a

hydrothermal system, in order to benefit from bonuses in temperature, depth and limited

natural permeability or fluid presence.

hydrothermal system, in order to benefit from bonuses in temperature, depth and limited

natural permeability or fluid presence.

One problem that has been reported during engineering of enhanced geothermal

reservoirs, is the occurrence of micro-seismic activity, probably associated with the hydraulic

fracturing works. These micro-earthquakes have a magnitude up to around 2 in the Richter

scale and pose no danger to existing buildings or structures. Whether they will also be

present during exploitation, and how they will evolve overtime, remains to be identified in

the field, but we anticipate that this micro-seismic activity should not be greater than the

one encountered in hydrothermal systems.

IntroductionLow Enthalpy Hydrothermal Fields

6

The positive environmental impact of all geothermal plants is attributed to foregone CO2 and

other emissions (e.g. CO, carbon particles, NOx, SOx), had the same quantity of energy been

produced by fossil fuels. However, in some low enthalpy geothermal fields the deep hot water

may contain dissolved CO2 in the form of bicarbonate ions. When these fluids are brought to the

surface and their pressure is lowered, they tend to deposit calcite and release CO2. Such fluids surface and their pressure is lowered, they tend to deposit calcite and release CO2. Such fluids

are usually located at the margins of larger hydrothermal systems. In Nigrita geothermal field of

Serres prefecture, Greece, which produces CO2 rich geothermal fluids of 60C, the correspond-

ing CO2 emissions are 15-20 times less than the ones released by fossil fuels when producing the

same amount of energy. The CO2 emissions from a geothermal field can be minimized by

engineering the exploitation scheme accordingly. For example, maximizing the energy extracted

from a given flow rate by placing the users in cascade, results in minimum CO2 emissions. In

agricultural uses, the geothermal CO2 can be directly released within the greenhouse, in order

to increase the growth rate of the plants and save fossil fuels.

IntroductionLow Enthalpy Hydrothermal Fields

7

Adverse environmental impact may occur from low enthalpy geothermal utilization, associated with the chemistry of the geothermal fluid, which may include considerable quantities of chloride, small quantities of boron, and traces of arsenic, ammonia, mercury, or heavy metals, making it unsuitable for disposal to the surface. The problem is effectively solved by reinjecting all the produced geothermal fluid to the same deep reservoir it originated from. This practice also has benefits to the the same deep reservoir it originated from. This practice also has benefits to the water replenishment of the deep system, improving sustainability and the economic life of the plant.

Other impact from long term low enthalpy geothermal utilization may be the dropping of water level of near surface aquifers and the flow reduction or dry-up of nearby springs and shallow water wells. The problem can be solved by reinjection, effective reservoir engineering and if the previous two measures do not solve the problem, by donating deep wells to affected water users.

IntroductionHigh Enthalpy Hydrothermal Fields

8

Like all forms of electric generation, both renewable and non-renewable,

geothermal power generation has environmental impacts and benefits.

Geothermal energywhether utilized in a binary, steam, or flash power

plant, cooled by air or water systemsis a clean, reliable source of electricity plant, cooled by air or water systemsis a clean, reliable source of electricity

with only minimal environmental impacts, even when compared with other

renewable energy sources.

In high enthalpy hydrothermal systems, the steam phase of the geothermal

fluid frequently contains small quantities of non-condensable CO2, the

quantity of which varies from field to field but it is limited to a few

percentage units, usually in the range 0,05-5%.

IntroductionHigh Enthalpy Hydrothermal Fields

9

Comparison of CO2 emissions between

geothermal and conventional power plants

Plant

Net

Power,

MWel

CO2,

% w/w

Conversion

efficiency

%

CO2emissions,

kg/kWhelMilos, Greece - 1,0 1,5 19,1* 0,10Milos, Greece - 1,0 1,5 19,1* 0,10

Lago 8,30 1,7 13,3 0,16

Monterotondo 8,19 1,6 13,2 0,16

Molinetto 17,95 4 17,7 0,29

Gabbro 16,52 12 14,6 1,05

Radicondou 36,89 5 19,0 0,34

Travale 40,75 5 21,0 0,31

Natural Gas 50 0,38

Diesel Oil 33 0,75

Coal 33 0,90*steam phase only

IntroductionEmissions

10

The visible plumes seen rising from some geothermal power

plants are actually water vapor emissions (steam), not smoke.

Because geothermal power plants do not burn fuel like fossil Because geothermal power plants do not burn fuel like fossil

fuel plants, they release virtually no air emissions. A case study

of a coal plant updated with scrubbers and other emissions

control technologies emits 24 times more carbon dioxide,

10,837 times more sulfur dioxide, and 3,865 times more nitrous

oxides per MWh than a geothermal steam plant.

Introduction

Emissions11

Emission Nitrogen oxide

(NOx)

Sulfur Dioxide

(SO2)*

Particulate Matter

(PM)

Carbon Dioxide

(CO2)

Sample Impacts Lung irritation,

coughing, smog

formation, water

quality

Wheezing, chest

tightness,

respiratory illness,

ecosystem damage

Asthma, bronchitis,

cancer,

atmospheric

deposition, visibility

Global warming

produced by CO2increases sea level,

flood risk, glacial

formation, water

quality

deterioration

respiratory illness,

ecosystem damage

atmospheric

deposition, visibility

impairment

increases sea level,

flood risk, glacial

melting

Geothermal

emissions (kg/MWh)0 0 0.16 0 0 40.28

Coal emissions

(kg/MWh)1.95 4.71 1.01 993.82

Emissions Offset by

Geothermal Use

(per yr)

32103 tons 78103 tons 17103 tons 16103 tons

*SO2 emissions derive from hydrogen sulfide emissions.

Introduction

Emissions12

Hydrogen Sulfide (H2S) is now routinely abated at geothermal power plants, resulting in the conversion of over 99.9% of the H2S from geothermal noncondensable gases into elemental sulfur, which can then be used as a non-hazardous soil amendment and fertilizer feedstock. Since 1976, H2S emissions have declined from 862 kg/hr to 91 kg/hr or less, although geothermal power production has increased from 500 megawatts (MW) to emissions have declined from 862 kg/hr to 91 kg/hr or less, although geothermal power production has increased from 500 megawatts (MW) to over 2,000 MW.

Mercury: Although mercury is not present in every geothermal resource, where it is present, mercury abatement equipment typically reduces emissions by 90% or more. The comparaLvely highest mercury emiNers, two facilities at The Geysers in California, release mercury at levels that do not trigger any health risk analyses under strict California regulations.

IntroductionAdditional Environmental Issues

13

Noise Pollution: Normal geothermal power plant operation typically produces less

noise than the equivalent produced near leaves rustling from breeze, according to

common sound level standards, and thus is not considered an issue of concern.

Water Use: Geothermal plants use 0.02 m3 of freshwater per MWh, while binary air-Water Use: Geothermal plants use 0.02 m of freshwater per MWh, while binary air-

cooled plants use no fresh water. This compares with 1.37 m3 per MWh used by

natural gas facilities.

Water Quality: Geothermal fluids used for electricity are injected back into geothermal

reservoirs using wells with thick casing to prevent cross-contamination of brines with

groundwater systems. They are not released into surface waterways. At The Geysers

facility, around 42 thousands m3 of treated wastewater from Santa Rosa are pumped

daily for injection into the geothermal reservoir. Injection reduces surface water

pollution and increases geothermal reservoir resilience.

IntroductionAdditional Environmental Issues

14

Land Use: Geothermal power plants can be designed to fit into their surrounding,

and can be located on multiple-use lands that incorporate farming, skiing, and

hunting. A geothermal facility uses 404 m2 of land per GWh, while a coal facility uses

3632 m2 per GWh. 3632 m per GWh.

Subsidence: Subsidence, or the slow, downward sinking of land, may be linked to

geothermal reservoir pressure decline. Injection technology, is an effective

mitigating technique.

Induced Seismicity: While earthquake activity, or seismicity, is a natural

phenomenon, geothermal production and injection operations have at times

resulted in low-magnitude events known as microearthquakes. These events

typically cannot be detected by humans, and are often monitored voluntarily by

geothermal companies.

IntroductionAdditional Environmental Issues

15

Geysers, Fumaroles, and Geothermal Resources: While almost all geothermal resources

currently developed for electricity production are located in the vicinity of natural geothermal

surface features, much of the undeveloped geothermal resource base may be found deep under

the Earth without any corresponding surface thermal manifestations. Geothermal surface

features, while useful in identifying resource locations, are not used during geothermal features, while useful in identifying resource locations, are not used during geothermal

development. (according laws and regulations to protect and preserve national parks and their

significant thermal features).

Impact on Wildlife and Vegetation: Before geothermal construction can begin, an environmental

review may be required to categorize potential effects upon plants and animals. Power plants

are designed to minimize the potential effect upon wildlife and vegetation, and they are

constructed in accordance with the regulations of the host state that protect areas set for

development.

Geothermal energy and the Environment

- Air Emissions -16

Geothermal power plants (GPP) release very few air emissions because they avoid

both environmental impacts associated with burning fuels as well as those associated

with transporting and processing fuel sources. GPP emit only trace amounts of NOx,

almost no SO2 or particulate matter, and small amounts of CO2. The primary pollutant almost no SO2 or particulate matter, and small amounts of CO2. The primary pollutant

some GPP must sometimes abate is H2S, which is naturally present in many

subsurface geothermal reservoirs. With the use of advanced abatement equipment,

emissions of H2S are regularly maintained below the valid standards.

Average life cycle emissions at coal facilities are substantially higher than their

average operational emissions which do not consider the effects of coal mining,

transport, construction, and decommissioning. Life cycle emissions from geothermal

facilities, in contrast, generally remain in the same range as operational emissions.

Life Cycle versus Operational Emissions, Coal Power Plants

17

Plant by Plant Comparison 18

Geothermal energy and the Environment

- Air Emissions -19

The visible plumes seen rising from water cooled GPP are actually water vapor emissions (steam), not smoke, and are caused by the evaporative cooling system.

Air cooled systems emit no water vapor, and thus Air cooled systems emit no water vapor, and thus blend easily into the environment. In a water cooling process, 50% or more of the geothermal fluid that enters the cooling tower is emitted to the atmosphere as water vapor, while the remainder recycles back into the reservoir. Geothermal water vapor emissions contain only trace amounts of the pollutants typically found in much greater quantities in coal and gas power plant emissions.

Nitrogen oxides (NOx)20

NOx are often colorless and odorless, or reddish brown as NO2. NOx form during

high temperature combustion processes from the oxidation of nitrogen in the air.

Motor vehicles are the major source of these pollutants, followed by industrial

fuel-burning sources such as fossil fuel-fired power plants (responsible for fuel-burning sources such as fossil fuel-fired power plants (responsible for

approx. of NOx emissions).

NOx contribute to smog formation, acid rain, water quality deterioration, global

warming, and visibility impairment. Health effects include lung irritation and

respiratory ailments such as infections, coughing, chest pain, and breathing

difficulty. Even brief exposure to high levels of NOx may cause human respiratory

problems, and airborne levels of NOx above the EPA established average

allowable concentration of 0.053 ppm can cause ecosystem damage.

NOx21

Because GPP do not burn fuel, they emit very low levels of NOx. In most cases, geothermal facilities emit no NOx at all. The small amounts of NOxreleased by some geothermal facilities result from the combustion of H S. result from the combustion of H2S. GPP are generally required by law to maintain H2S abatement systems that capture H2S emissions and either burn the gas or convert it to elemental sulfur. During combustion, small amounts of NOx are sometimes formed, but these amounts are miniscule. Average NOx emissions are zero.

Coal, oil, and geothermal reported as average existing power plant

emissions; natural gas reported as average existing steam cycle, simple gas

turbine, and combined cycle power plant emissions.

Hydrogen Sulfide (H2S)22

H2S is a colorless gas that is harmless in small quantities, but is often regarded as an

annoyance due to its disLncLve - rotten-egg smell. H2S can be lethal in high doses. Natural

sources of H2S include volcanic gases, petroleum deposits, natural gas, geothermal fluids, hot

springs, and fumaroles. H2S may also form from the decomposition of sewage and animal

manure, and can be emitted from sewage treatment facilities, aquaculture facilities, pulp and manure, and can be emitted from sewage treatment facilities, aquaculture facilities, pulp and

paper mills, petroleum refineries, composting facilities, dairies, and animal feedlot operations.

Individuals living near a gas and oil drilling operation may be exposed to higher levels of H2S.

Anthropogenic (manmade) sources of H2S account for approximately 5% of total H2S

emissions. Health impacts from high concentrations include nausea, headache, and eye

irritation; extremely high levels can result in death. H2S remains in the atmosphere for about

18 hours. Though H2S is not a criteria pollutant, it is listed as a regulated air pollutant.

H2S23H2S remains the pollutant generally considered to be of greatest concern for the geothermal community. However, it is now routinely abated at GPP. The two most commonly used vent gas H2S abatement systems are the Stretfordand LO-CAT. Both systems convert over 99.9% of the H2S from geothermal noncondensable gases to elemental sulfur, which can then be used as a soil amendment and fertilizer feedstock. The cost to transport and sell the sulfur noncondensable gases to elemental sulfur, which can then be used as a soil amendment and fertilizer feedstock. The cost to transport and sell the sulfur as a soil amendment is about equal to the revenue gained from the transaction.

As a result of abatement measures, geothermal steam- and flash-type power plants produce only minimal H2S emissions. Binary and flash/binary combined cycle GPP do not emit any H2S at all.

Sulfur Dioxide (SO2)24

SO2 belongs to the family of SOx gases that form when fuel containing sulfur (mainly coal and

oil) is burned at power plants. Fossil fuel-fired power plants are responsible for the greatest

part of the SO2 emissions. High concentrations of SO2 can produce temporary breathing

impairment for asthmatic children and adults who are active outdoors. Health impacts from

short-term exposures include wheezing, chest tightness, shortness of breath, aggravation of short-term exposures include wheezing, chest tightness, shortness of breath, aggravation of

existing cardiovascular disease, and respiratory illness. SO2 emissions injure vegetation,

damage freshwater lake and stream ecosystems, decrease species variety and abundance, and

create hazy conditions.

While geothermal plants do not emit SO2 directly, once H2S is released as a gas into the

atmosphere, it spreads into the air and eventually changes into SO2 and sulfuric acid.

Therefore, any SO2 emissions associated with geothermal energy derive from H2S emissions.

When comparing geothermal energy to coal, the average geothermal generation of 15 TWh

avoids the potential release of 78000 tons of SO2 per year.

SO225

SO2 comparison

*Calculation converts H2S to SO2for comparison only

Particulate Matter (PM)26

PM is a broad term for a range of substances that exist as discrete particles. PM

includes liquid droplets or particles from smoke, dust, or fly ash.

Primary particles such as soot or smoke come from a variety of sources where fuel is

burned, including fossil fuel power plants and vehicles. burned, including fossil fuel power plants and vehicles.

Secondary particles form when gases of burned fuel react with water vapor and

sunlight. Secondary PM can be formed by NOx, SOx, and Volatile Organic

Compounds (VOCs).

Large particulates in the form of soot or smoke can be detected by the naked eye,

while small particulates (PM2.5) require a microscope for viewing. PM10 refers to all

particulates less than or equal to 10 microns in diameter of particulate mass per

volume of air.

PM27

PM is emitted through the full process of fossil fuel electricity production, particularly

coal mining. Health effects from PM include eye irritation, asthma, bronchitis, lung

damage, cancer, heavy metal poisoning, and cardiovascular complications.

PM contributes to atmospheric deposition, visibility impairment, and aesthetic PM contributes to atmospheric deposition, visibility impairment, and aesthetic

damage.

Although coal and oil plants produce hundreds of tons on an annual basis, GPP emit

almost no PM. Water-cooled GPP do emit small amounts of PM from the cooling

tower when steam condensate is evaporated as part of the cooling cycle. However, the

amount of PM given off from the cooling tower is quite small when compared to coal

or oil plants which have burning processes in combination with cooling towers.

PM comparizon28

Comparing pulverized coal boiler, natural gas

combined cycle, and average existing power

plant, geothermal.

Carbon dioxide (CO2)29Carbon dioxide, a colorless, odorless gas, is released into the atmosphere as a

byproduct of burning fuel. While CO2 emissions are also produced by natural sources,

most experts agree that increased atmospheric CO2 concentrations are caused by

human fossil fuel burning. Concentrations in the atmosphere have increased by

approximately 20% since 1960. The increase in CO is typically attributed to power approximately 20% since 1960. The increase in CO2 is typically attributed to power

plant (primarily coal) and vehicle emissions, and secondarily to deforestation and

land-use change. About 37% of incremental CO2 accumulation is caused by electric

power generation, mainly from fossil fuels. While CO2 does not pose any direct

human health effects - humans exhale CO2 with every breath experts generally

agree that global warming poses significant environmental and health impacts,

including flood risks, glacial melting problems, forest fires, increases in sea level, and

loss of biodiversity.

CO230

Geothermal plants do emit CO2, but in quantities that are small compared to fossil

fuel-fired emissions. Some geothermal reservoir fluids contain varying amounts of

certain noncondensable gases, including CO2.

Geothermal steam is generally condensed after passing through the turbine.

However, the CO does not condense, and passes through the turbine to the exhaust However, the CO2 does not condense, and passes through the turbine to the exhaust

system where it is then released into the atmosphere through the cooling towers.

The amount of CO2 found in geothermal fluid can vary depending on location, and

the amount of CO2 actually released into the atmosphere can vary depending on

plant design. This makes it difficult to generalize about the amount of CO2 emitted by

an average GPP. For example, binary plants with air cooling are in a closed loop

system and emit no CO2 because in this system the geothermal fluids are never

exposed to the atmosphere.

CO2 comparison 31

Despite these disparities, GPP will emit

only a small fraction of the CO2emitted by traditional power plants on

a per-MWh basis. Noncondensable

gases such as CO2 make up less than gases such as CO2 make up less than

5% by weight of the steam phase of

most geothermal systems. Of that 5%,

CO2 typically accounts for 75% or more

of noncondensable gas by volume.

Because of the low level of CO2 emissions, geothermal power produc-

tion currently prevents the emission of

22 million tons of CO2 annually when

compared to coal production.

Mercury (Hg)32

The majority of mercury emissions derive from natural sources. Hg occurs naturally in soils,

groundwater, and streams, but human activity can release additional Hg into the air, water,

and soil. Coal-fired power plants are the largest source of additional Hg of any energy source,

because the Hg naturally contained in coal is released during combustion. Currently, the coal

industry contributes for 1/3 of the anthropogenic mercury emissions. industry contributes for 1/3 of the anthropogenic mercury emissions.

Mercury emissions from coal vary both day to day and from plant to plant. Snapshot Hg

emissions information, taken over a 1-2 hour period, does not always accurately reflect long

term Hg emissions-hourly averages can vary by almost an order of magnitude. In addition, Hg

emissions from certain types of coal plants, such as bituminous plants, tend to be greater than

from other types of coal plants. It is estimated that bituminous plants emit 52% of coal

mercury emissions, while lignite coal plants emit only 9%. Those plants with emissions

technologies in place, such as combined selective catalytic reduction (SCR) and wet flue gas

desulphurization (FGD), tend to emit the lowest levels of mercury.

Hg33

Hg emissions from power plants pose a significant risk to human health.

When Hg enters water, biological processes transform it to a highly toxic

form, methyl mercury, which builds up in fish and animals that eat fish.

People are exposed to Hg primarily by eating fish or by drinking contaminated People are exposed to Hg primarily by eating fish or by drinking contaminated

water. Hg is especially harmful to women.

Hg is not present in every geothermal resource. However, if Hg is present in a

geothermal resource, using that resource for power production could result

in mercury emissions, depending upon the technology used. Because binary

plants pass geothermal fluid through a heat exchanger and then return all of

it to the reservoir, binary plants do not emit any mercury.

Hg34

Mercury abatement measures are already in place at most geothermal facilities.

The abatement measures that reduce mercury also reduce the emissions of sulfur

generated as a byproduct of hydrogen sulfide abatement: after hydrogen sulfide is

removed from geothermal steam, the gas is run through a mercury filter that removed from geothermal steam, the gas is run through a mercury filter that

absorbs mercury from the gas. In removing mercury, the sulfur that is created from

the abatement process can then be used as an agricultural product. The rate of

mercury abatement within a facility, which varies according to the efficiency of the

activated carbon mercury absorber, is typically near 90%, and is always efficient

enough to ensure that the sulfur byproduct is not hazardous. The activated carbon

media is changed out periodically and is disposed of as a hazardous waste. The

amount of hazardous waste reduction is thousands of tons/year.

Total Organic Gases & Reactive Organic Gases35

GPP may emit small amounts of naturally occurring hydrocarbons such as methane (CH4).

CH4 is reported in Total Organic Gases (TOG). 10% of TOGs are assumed to be Reactive

Organic Gas (ROG) emissions. TOGs consist of all compounds containing hydrogen and

carbon, while ROGs consist of organics with low rates of reactivity. CH4 is the primary

TOG emitted by geothermal plants, followed by ethane and propane. The EPAs inventory TOG emitted by geothermal plants, followed by ethane and propane. The EPAs inventory

of CH4 emission from electric plants does not list geothermal, confirming that CH4emissions from geothermal are generally insignificant. In contrast, natural gas facilities

emit 19% of domestic anthropogenic CH4, while coal mining and production accounts for

around 20%. Waste management accounts for the largest percentage of anthropogenic

methane emissions, at over 26%. CH4 emission estimates are uncertain, however,

because they are usually accidental or incidental to biological processes, and they are not

always present in geothermal systems.

TOGs and ROGs36

Other ROGs, such as benzene, a known carcinogen, are generally not of concern to the geothermal community, as they are injected back into the system. Benzene emissions released at most geothermal facilities, including the Salton Sea in southern California, have never been high enough to trigger a risk assessment under California EPA been high enough to trigger a risk assessment under California EPA exposure level standards. Although the Heber geothermal facility in southern California was required to conduct quarterly benzene cooling tower analysis as a stipulation in their permit agreement,90 analyses indicated that benzene comprises less than 1% of cooling tower gases.

Ammonia (NH3)37Naturally occurring ammonia (NH3) is emitted at low levels by geothermal facilities, with more concentrated amounts emitted by certain plants at The Geysers. While livestock is responsible for almost half of ammonia emissions, geothermal accounts for only a fraction of ammonia emissions, at substantially lower than one percent. Additional sources include fertilizers, crops, and biomass burning. Emitted ammonia can combine with water to substantially lower than one percent. Additional sources include fertilizers, crops, and biomass burning. Emitted ammonia can combine with water to form NH4OH (ammonium hydroxide). If it lasts long enough in the environment, ammonia may combine with nitrogen oxide to form particulate (ammonium nitrate) or if there are no acid gasses present in the atmosphere, it will be absorbed into the soil and taken up by green plants. Experts generally concur that ammonia is released as hydrated ammonia, and depending upon the environment, is absorbed in soil to become part of the nitrogen cycle.

Boron38

Boron, an element found in volcanic spring waters, does not exist naturally in its elemental

form, but is commonly found as a mineral salt, borax, in dry lake evaporate deposits. Boron

is only toxic when high concentrations are ingested. When present in soil at low

concentrations, boron is essential to the normal growth of plants.

In geothermal steam systems, boron is present in the steam as highly soluble boric acid.

When combined with ammonia, it often forms white crystalline salt deposits on equipment

exposed to geothermal steam. Because of its high solubility, nearly all borate entering a

geothermal plant will dissolve in the steam condensate, where it exits the plant through

cooling tower blowdown and is injected back into the steam reservoir. New geothermal

plants are now required to install high efficiency drift eliminators for particulate control

regardless of boron content in the water, and these eliminators reduce boron emissions.

Boron salt compounds may be emitted in cooling tower drift, but boron emissions are

generally not regulated, as does not cause any environmental impact.

Air emissions - Conclusions39

Total noncondensable gas emissions from geothermal resources typically make up less than 5% of the total steam emitted, whereas air emissions from facilities such as coal contain much higher percentages of emissions. Geothermal air emissions are significantly lower than those of an power plant. For example, the geothermal sulfur dioxide those of an power plant. For example, the geothermal sulfur dioxide equivalent, derived from hydrogen sulfide emissions, is one of the most significant pollutants emitted from geothermal power plants. Even so, sulfur dioxide emitted by geothermal facilities, at 0.16 kg/MWh, represents only a fraction of the 2.74 kg/MWh of sulfur dioxide generated by the average power plant.

Air emissions summary40

kg/MWh NOx SO2 CO2 PM

Coal 1.95 4.71 993.82 1.01

Coal, life cycle emissions 3.35 6.71 NA 9.21

Oil 1.81 5.44 758.40 NA

Natural Gas 1.34 1.00 550 0.06Natural Gas 1.34 1.00 550 0.06

EPA Listed Average of all U.S.

Power Plants1.34 2.74 631.62 NA

Geothermal (flash) 0 0.16 27.21 0

Geothermal (binary and

flash/binary)0 0 0 negligible

Geothermal (Geysers steam) 0.0005 0.0001 40.28 negligible

Solid and Liquid Waste41

Generally, air emissions are the most significant environmental issue of concern. Solid wastes discharged from geothermal power plants are nonhazardous and in low quantities. quantities.

The substances listed are typically either too low to cause any concern, or are recycled through the system and do not make contact with water, land, or air. Solid and liquid waste substances are included to provide a comprehensive review of the environmental aspects of geothermal energy.

Solid and Liquid WasteArsenic

42

Arsenic, in its pure form, is a gray, crystalline solid, but can be found in

various forms in the natural environment in combination with other

elements. Arsenic is produced naturally in the Earths crust and can be

emitted during volcanic eruptions. It is also produced in fossil fuel emitted during volcanic eruptions. It is also produced in fossil fuel

processing and in the production of pesticides, wood preservatives,

glass, and other materials. It is a known human carcinogen. Additional

health effects include sore throat, irritated lungs, nausea, vomiting,

decreased production of red and white blood cells, abnormal heart

rhythm, damage to blood vessels, and skin pigmentation abnormalities.

Arsenic43

Geothermal plants are not considered to be high arsenic emitters even though arsenic is common to volcanic systems. When arsenic is present in a geothermal system, it typically ends up in the solid form in the sludge and scales associated with production and hydrogen sulfate abatement. Arsenic emission levels have been well documented over the years through two emissions inventories in California: the Air Toxic Hot Spots Program and emission levels have been well documented over the years through two emissions inventories in California: the Air Toxic Hot Spots Program and The Geysers Air Monitoring Programs (GAMP), both of which have shown limited arsenic emissions. Results of these programs have shown arsenic emissions levels from geothermal power plant to be very small, if they are even detectable. A study of The Geysers showed that arsenic emissions were not of significant concern: the average level at The Geysers, at around 1.6 ngm-3, was found to be very close to the statewide average of 1.5 ng m-3.

Solid and Liquid WasteSilica and other waste products

44

Silica, an abundant element that is the primary component of sand, is a byproduct of

geothermal power production from certain brine reservoirs. Silica is typically dewatered, and

the silica sludge is disposed of off site. Silica is only considered a potential hazard when found in

high concentrations in the workplace, but it poses no environmental risk. Silica is found in the

effluents, or treated wastewaters, that are the byproducts of drilling operations in some effluents, or treated wastewaters, that are the byproducts of drilling operations in some

resources. Concentrations of silica are low enough in geothermal facilities that workers are not

at risk. Other geothermal effluents are generally considered to be harmless, and even, at times,

beneficial to the environment.

The primary "waste" in geothermal operations is drilling cuttings, comprised primarily of

bentonite, a naturally occurring clay. Wastes from drilling activities, mud and cuttings, are stored

in what are known as sumps for disposal. Sumps provide secure storage for drilling mud and

cuttings. They are typically lined with impervious materials to prevent leaching.

Noise Pollution

45

Sound is measured in units of

decibels (dB), but for environ-

mental purposes is usually

measured in decibels A-

weighted (dBA).

Common sound levels

weighted (dBA).

A-weighting refers to an

electronic technique which

simulates the relative response

of the human auditory system to

the various frequencies

comprising all sounds.

Noise Pollution46

Geothermal power plants can operate in compliance with the applicable

regulations and are not considered a noise nuisance in surrounding residential

communities. All power facilities must meet local noise ordinances according

to the phase of construction and operation.

Noise pollution from geothermal plants is typically considered during three

phases: the well-drilling and testing phase, the construction phase, and the

plant operation phase.

During the construction phase, noise may be generated from construction of

the well pads, transmission towers, and power plant. During the operation

phase, the majority of noise is generated from the cooling tower, the

transformer, and the turbine-generator building.

Noise Pollution47

Construction is one of the noisiest phases of geothermal development, but

even construction noise generally remains below the 65 dBA. Furthermore,

noise pollution associated with the construction phase of geothermal

development, as with most construction, is a temporary impact that ends development, as with most construction, is a temporary impact that ends

when construction ends. Well pad construction can take anywhere from a

few weeks or months to a few years, depending upon the depth of the

well. In addition, construction noise pollution is generally only an issue

during the daytime hours and is not a concern at night.

Noise Pollution48

The well-drilling and testing phase of geothermal development generally does not exceed the

noise regulations, they are temporary, and the noise pollution they produce is not permanent.

However, well-drilling operations typically take place 24 hrs per day, seven days a week. This

temporary noise pollution can last anywhere from 45 to 90 days per well.

Noise from normal power plant operation generally comes from the three components of the Noise from normal power plant operation generally comes from the three components of the

power plant: the cooling tower, the transformer, and the turbine-generator building. The

produced noise is in range of whisper.

Several noise muffling techniques and equipment are available for geothermal facilities. During

drilling, temporary noise shields can be constructed around portions of drilling rigs. Noise

controls can also be used on standard construction equipment, impact tools can be shielded,

and exhaust muffling equipment can be installed where appropriate. Because turbine-generator

buildings are usually designed to accommodate cold temperatures, they are typically well-

insulated acoustically and thermally, and equipped with noise absorptive interior walls.

Water Quality and Use49

Geothermal water (GW) is a hot, often salty, mineral-rich liquid withdrawn

from a deep underground reservoir. The steam that is "flashed" from the hot

water is used to turn turbines and generate electricity. The remaining water,

along with the condensed steam, is then injected back into the geothermal along with the condensed steam, is then injected back into the geothermal

reservoir to be reheated. In water cooled systems, 50% or more of the liquid

is lost to the atmosphere in the form of steam, and the remainder is injected

back into the system. Because the GW in a binary, air cooled plant is

contained in a closed system, binary power plants do not consume any water.

In a geothermal facility, GW is isolated during production, injected back into

the geothermal reservoir, and separated from groundwater by thickly encased

pipes, making the facility virtually free of water pollutants.

Water Quality and Use50

Most geothermal reservoirs are found deep underground, well

below groundwater reservoirs. As a result, these deep reservoirs

pose almost no negative impact on water quality and use. Anyway,

potable groundwater and clean surface water are important potable groundwater and clean surface water are important

resources that require continued attention as the use of domestic

geothermal resources grows.

Water Quality and Use51

Geothermal steam and hot water can reach the surface in two ways: through naturally

occurring surface features such as geysers and fumaroles, or through man-made wells that are

drilled down into the reservoir to capture the Earths energy for electricity. In either case,

these natural geothermal fluids contain varying concentrations of potentially toxic minerals

and other elements and are extremely hot when they reach the surface of the Earth. For these and other elements and are extremely hot when they reach the surface of the Earth. For these

reasons, GWs can be dangerous to humans and surrounding ecosystems. This is just one of the

reasons that geothermal fluids used for electricity are injected back into geothermal reservoirs

and are not allowed to be released into surface waterways. When geothermal fluids are inject-

ed back into a geothermal system, the fluids are isolated from shallow groundwater by thick

well casing. Injection typically takes place in separate wells that are designed to properly

handle the chemistry of the injection fluids. In addition, geothermal developers manage geo-

thermal fluids in order to minimize potential impacts. Benefits of injection include enhanced

recovery of geothermal fluids, reduced subsidence and safe disposal of geothermal fluids.

Water Quality and Use52

Occasionally, geothermal effluents, if stored rather than injected back into the system, deliver beneficial environmental effects. For example, injection was banned at the Amedee geothermal field in northeastern California because the effluent, stored in a holding tank, produced a diverse, thriving wetland. In another case, an evaporative pond at a Mexican geothermal facility was found to be occupied by 34 species of birds.species of birds.

The Icelandic tourist attraction, the Blue Lagoon (a turquoise body of mineral rich water) was actually created by geothermal water discharged from a power plant. Not only is the Blue Lagoon safe for swimming, but the waters are also touted as soothing and as sources of curative powers.

Although most geothermal community agrees that injection is the most environmentally beneficial method of disposing of geothermal fluids, there are instances where other beneficial approaches have been taken.

Water Quality and Use53

Blue Lagoon: Tourist Attraction and

Geothermal WastewaterGeothermal Wastewater

Wastewater injection54

Geothermal plants have the potential to improve local water quality. So-called

waste water injection projects serve the dual purpose of eliminating

wastewater, which would otherwise be dumped into local waterways, and

rejuvenating geothermal reservoirs with new water sources. rejuvenating geothermal reservoirs with new water sources.

Although geothermal development does not contaminate groundwater, like any

form of development, it has some impact on local water use. For geothermal

developers, most water impacts occur during construction and are only

temporary. However, regardless of the nature or degree of water use impacts,

geothermal developers should prioritize sound reservoir management practices

that benefit geothermal operation and preventatively minimize potential impact.

Wastewater injection55

Geothermal power plants do use surface or groundwater during the construction and

operation of the power plant as well as during well drilling to sustain operations. These

uses, while typically not a significant concern as they do not dramatically decrease the

amount of ground and surface water available for potable uses, should be taken into

account during the development of geothermal resources.account during the development of geothermal resources.

Fossil fuel plants, in contrast to geothermal facilities, must contend with water

discharge and thermal pollution throughout the life of the plant, and waste heat from

fossil fuel and nuclear facilities can devastate the animals and plants that inhabit local

water bodies. In addition, both coal and nuclear plants use more water per MWh than

geothermal facilities in cooling their high-temperature fluids. Heated water is often

dumped into local bodies of water, creating environmental disruption from the intake

and heating processes.

56

Freshwater Use Comparison

The geothermal water use

figure does not include

geothermal fluid, as this liquid

Wastewater injection

geothermal fluid, as this liquid

is injected back into the

system and is not withdrawn

from existing freshwater

resources.

Wastewater injection57

During normal operations, liquid wastes from drilling activities are stored in lined sumps before being properly disposed of in accordance with state regulations. Accidental spills of geothermal waters may occur due to well blowouts during drilling, leaking piping or wellheads, or overflow from well sumps. However, these incidents are wellheads, or overflow from well sumps. However, these incidents are rare, and are generally prevented through sound management practices by geothermal developers. Overall, any negative effect of geothermal development on surface waterways would be accidental, and even then, by following federal and state laws, their impact would be kept minimal.

Land Use58

Geothermal power plants can be design-

Flash/binary Puna Geo Venture facility, located in

Hawaii. This plant blends into its surroundings and

produces no steam plumes, while still utilizing high

temperature resources.

Geothermal power plants can be design-

ed to blend-in to their surrounding

more so than many other types elec-

tricity-producing facilities. Binary and

flash/binary power plants normally emit

no visible steam or water vapor plumes,

and flash and steam plants produce

minimal visual impacts.

Land Use59

Geothermal facilities are often located on lands that have multiple-use capabilities. Case study at the geothermal facilities of Salton Sea and Imperial Valley in Southern California - at these sites, several aquaculture operations use geothermal water to control the water temperatures, improve fish and fish culture facilities, and extend the fish growth season. In addition, these power plants in the Imperial Valley are surrounded by productive farm land. surrounded by productive farm land.

Another geothermal plant, the Mammoth power plant in Northern California, is located only miles from the Mammoth Ski Resort and yet does not detract from the natural beauty of the area. In addition, The Geysers field teems with wildlife and still serves as a prime hunting ground for the individuals and hunting clubs that own much of the land. Finally, a 1995 study found that geothermal resource use can beneficially influence the state of health of the population and the environment by reducing deforestation and air emissions.

Land Use60

Imperial Valley Power Plant Next to

Productive Farmland

Land Use61

While some fossil-fuel energy sources, such as coal, use up large swaths of land in the mining of their fuel, geothermal plants minimize the total amount of land used by only building the plant along with the number of well pads needed to support operation. It is important to keep in mind that the land impact of renewable energy development and use is much less damaging than the impact caused by fossil fuel development and use. Coal mining impact of renewable energy development and use is much less damaging than the impact caused by fossil fuel development and use. Coal mining requires the transportation of huge amounts of dirt and rock, sometimes into streams, and causes disruption of water systems through acid drainage, deforestation, and damage to ecosystems. Nuclear facilities require the safe maintenance of huge amounts of radioactive waste. Over 30 years, the period of time commonly used to compare life cycle impacts of different power sources, geothermal uses less land than many other sources.

Land Use62

30 Year Land Use

* Includes mining.

**Assumes central station photovoltaic project, not rooftop PV systems.

*** Land actually occupied by turbines and service roads.

Land Use63

GPP impose minimal visual impacts on their surroundings when compared to typical fossil-fuel

plants. Some of the key visual quality effects related to geothermal development are the

presence of steam plumes, night lighting on the wellfield and power plant, and visibility of the

transmission line. Fossil fired power plants have all of these visual effects as well. The majority

of geothermal visual impacts can be mitigated to reduce their effects. Detailed site planning, of geothermal visual impacts can be mitigated to reduce their effects. Detailed site planning,

facility design, materials selection, revegetation programs, and adjustment to transmission line

routing are all key aspects of geothermal operations that can reduce the visual impacts of the

facility. Today, many geothermal operators already employ these mitigation techniques to

reduce their facilities visual impact.

Other visual impacts are only of concern on a temporary basis, such as construction

equipment. Construction vehicles, drill rigs, and other heavy equipment would have a negative

impact on the visual quality of the area for a limited amount of time.

Land UseSubsidence

64

Subsidence is most commonly thought of as the slow, downward sinking of the land surface. Other types of ground deformation include upward motion (inflation) and horizontal movements. In some cases, subsidence can damage facilities such as roads, buildings and irrigation systems, or even cause tracts of land to become submerged by nearby bodies of water. Although it can occur naturally, subsidence can also occur as a result of the extraction of of land to become submerged by nearby bodies of water. Although it can occur naturally, subsidence can also occur as a result of the extraction of subsurface fluids, including groundwater, hydrocarbons, and geothermal fluids. In these cases, a reduction in reservoir pore pressure reduces the support for the reservoir rock itself and for the rock overlying the reservoir, potentially leading to a slow, downward deformation of the land surface. In most areas where subsidence has been attributed to geothermal operations, the region of Earth deformation has been confined to the wellfield area itself, and has not disturbed anything off-site.

Land UseSubsidence

65

While subsidence can be induced by thermal contraction of the reservoir due to extraction and natural recharge, properly placed injection reduces the potential for subsidence by maintaining reservoir pressures. At fields produced from sedimentary rocks where the porosity and permeability is primarily between rock grains, injection can successfully mitigate for subsidence.

Naturally-occurring subsidence most frequently takes place in areas that are Naturally-occurring subsidence most frequently takes place in areas that are tectonically active such as volcanic regions and fault zones. Subsidence can also typically occur in areas where sedimentary basins are filled with unconsolidated sands, silts, clays and gravels. Most known geothermal resources are located in areas that are tectonically active, and may experience natural subsidence. Because geothermal operations occur at tectonically active sites, it is sometimes difficult to distinguish between induced and naturally occurring subsidence. Subsidence related to geothermal development is more likely in areas where the geothermal reservoir occurs in weak, porous sedimentary or pyroclastic formations.

Land UseSubsidence

66

In cases where subsidence may be linked to geothermal reservoir pressure decline, injection is an effective

mitigating technique. By injecting spent geothermal brines back into the reservoir from which they came,

reservoir pressure is stabilized. This approach has helped to maintain the pressure of geothermal

reservoirs and can prevent or mitigate for subsidence at geothermal development sites.

Injection technology has not always been utilized in other parts of the world, and therefore subsidence has Injection technology has not always been utilized in other parts of the world, and therefore subsidence has

been a larger issue at some geothermal developments overseas. The most commonly referenced case of

major subsidence at a geothermal field is the Wairakei geothermal field in New Zealand. At this field,

which has been operating since the late 1950s, geothermal fluids were not routinely injected back into the

geothermal reservoir. Although limited injection began in the late 1990s at Wairakei, most subsidence had

already occurred at this point. Long-term extraction of fluids without injection resulted in high subsidence

rates in some areas near the production field, and a lower rate of subsidence across a much wider area. In

the United States, as well as most other geothermal fields worldwide, injection of spent geothermal brines

begins immediately after a plant comes on-line, and continues through the life of the plant.

Land UseInduced Seismicity

67

Earthquake activity, or seismicity, is generally caused by displacement across active faults in tectonically active zones. An earthquake occurs when a body of rock is ruptured and radiates seismic waves that shake the ground. Although it typically occurs naturally, seismicity has at times been induced by human activity, including the development of geothermal fields, through both production and injection operations. In these cases, the resulting seismicity has been low-magnitude events operations. In these cases, the resulting seismicity has been low-magnitude events known as microearthquakes. Earthquakes with Richter magnitudes below 2 or 3, which are generally not felt by humans, are called microearthquakes. These microearthquakes sometimes occur when geothermal fluids are injected back into the system, and are centered on the injection site. The microearthquakes sometimes associated with geothermal development are not considered to be a hazard to the geothermal power plants or the surrounding communities, and will usually go unnoticed unless sensitive seismometers are located nearby.

Land Use

Induced Seismicity68

Much like subsidence, seismicity typically takes place in areas with

high levels of tectonic activity, such as volcanic regions and fault

zones. Because geothermal operations usually take place in areas that

are also tectonically active, it is often difficult to distinguish between are also tectonically active, it is often difficult to distinguish between

geothermal-induced and naturally occurring events. Many regions

where geothermal development has occurred or has been planned

are known as areas with high levels of fault activity. These regions

frequently experience earthquakes of various magnitudes, though few

are felt by humans.

Land UseLand slides

69

The extent to which geothermal development induces landslides is unclear, as landslides, which occur naturally in certain areas of geothermal activity such as volcanic zones, are produced by a combination of events or circumstances rather than by any single specific action. While field construction operations can trigger landslides, local geological preconditions must already exist in order for landslides to occur. Though construction operations can trigger landslides, local geological preconditions must already exist in order for landslides to occur. Though landslides are rare, when they occur they are small enough to be confined entirely to the wellfield area of a geothermal facility. Geothermal areas with landslide hazards can be properly managed through detailed hazard mapping, groundwater assessment, and deformation monitoring, among other management techniques. Because landslides always present warning signs, such techniques ensure that landslides can be avoided on geothermal lands.

Geysers, Fumaroles and Geothermal Resources70

Geothermal resources are often

discovered under certain land

features such as geysers, fumaroles,

hot springs, mud pools, steaming

ground, sinter, and travertine. ground, sinter, and travertine.

Geysers are hot springs where hot

water, steam, or gas periodically

erupts, while fumaroles vent gas and

steam. The word geyser derives

from the Icelandic word, geysir,

which means, the gusher.

Geothermal Surface Features

Geysers, Fumaroles and Geothermal Resources71

There are concerns that such land features will be drastically altered or destroyed as a

result of geothermal development. In some cases, both during past geothermal

development and geothermal development overseas, it is true that land features have

been altered by geothermal development. However, through the evolution of geothermal

development, developers have come to understand the best management practices that development, developers have come to understand the best management practices that

reduce surface feature impact, and have employed preventative mitigation measures that

reduce potential impact to surface features before they arise. In addition, monitoring

programs for significant surface features are required by law, and geothermal development

in areas where surface features may be adversely affected is forbidden. The current status

of geothermal development shows that little alteration of land features has occurred in

recent years as a result of sound geothermal management practices and law compliance.

Impact on Wildlife and Vegetation72

Geothermal development poses only minimal impact to wildlife and vegetation in the surrounding area when compared with alternatives such as coal. It should be noted that geothermal facilities must sometimes be built in more sensitive areas than coal plants. However, increased sensitivity leads to increased mitigation and surveillance in increased sensitivity leads to increased mitigation and surveillance in these areas. Before geothermal construction can even begin, an environmental review may be required to categorize potential effects upon plants and animals. While any disruption of land that results from power plant construction has the potential to disturb habitat, geothermal plants, like any type of power plant, must comply with a host of regulations that protect areas set for development.

Impact on Wildlife and Vegetation73

Geothermal plants are designed to minimize the potential effect upon wildlife and vegetation: pipes are insulated to prevent thermal losses, power plants are fenced in so as to prevent wildlife access, spill containment systems with potential to hold 150 percent of the potential maximum spill are put in place, and areas with high concentrations of wildlife or vegetation specific to an area are avoided. Because geothermal plants avoid much of the additional disruption caused by mining coal and geothermal plants avoid much of the additional disruption caused by mining coal and building roads to transport it, the construction of a geothermal plant reduces the overall impact on wildlife and vegetation species from energy production. A typical 500 MW coal plant, for example, can disrupt 21 million fish eggs, fish larvae, and juvenile fish from water usage alone during normal operation, as the 8.3 millions m3

of water required each year to create steam for turbine generation is extracted from nearby water bodies rich with fish species. Many species habitats are restricted by road construction or eliminated altogether by mining activities related to fossil fuel production.

Summary74

Despite improvements in coal, natural gas, and oil power plant technology, fossil fuel

combustion continues to produce more air pollution than any other single source. They

are main contributors for water pollution, SO2 emissions and take great part in the NOx

and CO emissions. These pollutants have been widely documented to cause a host of and CO2 emissions. These pollutants have been widely documented to cause a host of

environmental and health problems, and climate change.

Although green power pollutes significantly less than fossil fuel sources, it is important to

note that all power generation impacts the environment, regardless of whether electricity

is derived from the combustion of fossil fuel or renewable sources. Impacts such as land

use, for example, cannot be avoided no matter what level of mitigation is employed. The

goal, instead of eliminating all impacts, should be to minimize impacts.

Summary Environmental Benefits of Geothermal Energy

75

Most important environmental benefits which support the expanded

geothermal power generation:

Geothermal energy is reliable

Geothermal energy is renewable Geothermal energy is renewable

Geothermal energy produces minimal air emissions and offsets the high

air emissions of fossil fuel-fires power plants

Geothermal energy can offset other environmental impacts

Geothermal energy is combustion free

Geothermal energy minimally impacts land

Geothermal energy is competitive with other energy technologies when

environmental costs are considered

Conclusion76

Abundant geothermal resources throughout the nations can provide an environmentally

friendly source of energy. Data compiled from a variety of sources point to geothermal

energy as an environmental option for new power and heat generation that is far better than

other energy sources such as fossil fuels. In addition, geothermal remains as environmentally

friendly as most other renewable sources, while simultaneously offering reliability and a friendly as most other renewable sources, while simultaneously offering reliability and a

source of baseload power that is unique among most other renewable options available.

While currently used at only a fraction of its potential, geothermal energy can substantially

contribute to the energy needs of the twenty-first century.

As geothermal energy production is refined and expanded, the benefits continue to grow.

With continued technological development, geothermal can be expanded all over the world,

and the already negligible environmental geothermal impacts can be reduced to nearly zero.

Geothermal energy can provide the clean, reliable, and plentiful renewable energy resource

for the world.